1. Field of the Invention
The present invention relates to motion error compensation for use with machine tool tables that are movable in two mutually perpendicular axes.
2. Description of the Prior Art
Control systems for controlling the position of a machine tool table, particularly in relation to adaptive control during machining, have been known. For example, U.S. Pat. No. 4,602,459 discloses a control system for precision machine tools that has a table adapted to be mounted onto an existing machine tool table and which provides a mounting that is specifically controlled by a piezoelectric actuator operated in an active closed loop system to maintain a set position without any backlash. The table disclosed in '459 comprises an extra structure over the existing machine tool table, which adds some extra cost, and in some applications the additional cost is objectionable. The extra structure does decrease the rigidity of the machine as well. CNC machine tools have existing controls for controlling the table position in two or more axes through a servo control arrangement, but errors in motions of the table are not adequately controlled for precise positioning of such table along the respective axes of movement, even when the actuators in both control axes are very accurate. The sensors do not sense errors caused by nonperfect table slides, so such errors are not compensated.